Gypsum additive to control mercury

ABSTRACT

Additives including sulfur-containing compounds are used in methods of treating synthetic gypsum. The additives can thermally stabilize heavy metals, such as mercury. This thermal stabilization reduces mercury release from the synthetic gypsum. Illustrative, non-limiting examples of sulfur-containing compounds include inorganic sulfides, organic sulfides, organic compounds containing nitrogen and sulfur, organic compounds containing oxygen and sulfur, and polymers containing sulfur.

BACKGROUND 1. Field of the Invention

The present disclosure generally relates to additives and methods forcontrolling mercury. More particularly, the disclosure relates tosulfur-containing compounds useful as mercury control additives.

2. Description of the Related Art

The Environmental Protection Agency (EPA) recently published the Mercuryand Air Toxics Rule (MATS Rule) that will require all electricitygenerating units (EGUs) that burn fossil fuels to reduce mercuryemissions levels. Many of these units currently use, or will use, wetflue gas desulfurizers (wFGDs) to meet acid gas or SOx emission limits.A wFGD contacts combustion gas with an aqueous alkaline solution, whichsolution may be composed of magnesium compounds, sodium compounds, andslurries of lime or limestone to capture and neutralize acid gases, suchas sulfur dioxide. The aqueous alkaline solution is commonly referred toas “wFGD liquor” or “scrubber liquor.” In a forced oxidation system,oxygen may be introduced into the wFGD liquor to oxidize sulfite tosulfate. In many cases, this forms gypsum (calcium sulfate), as thefinal byproduct of scrubbing. Other systems may utilize inhibited ornatural oxidation scrubbing which results in sulfite salts or mixedsulfite/sulfate salts as byproduct.

Mercury entering EGUs as a contaminant of the fuel is released duringcombustion. Combustion gases exiting the boiler may contain mercury inthree forms: particulate, oxidized, and elemental. Particulate mercurycan be captured by particulate control devices such as electrostaticprecipitators (ESPs) and fabric filters (FF). Oxidized mercury iswater-soluble so wFGDs can absorb the oxidized mercury from thecombustion gas into the liquid phase. Elemental mercury, which isinsoluble in water, is difficult to capture using existing air qualitycontrol devices. Consequently, mechanical methods, such as fixed bedcatalysts (e.g., SCRs) and chemical additives (e.g., calcium bromide,hydrogen bromide, ammonium chloride) have been developed that oxidizeelemental mercury in the gas phase for subsequent capture with a wFGD.The captured mercury leaves the process via wFGD blow down.

As oxidized mercury is water soluble, wFGDs are theoretically capable ofcapturing nearly 100% of the oxidized mercury in a combustion gas.However, data collected by the Department of Energy (DOE) as well asnumerous laboratory and commercial studies have shown lower captureefficiencies. The lower efficiencies are the result of reduction ofoxidized mercury to elemental mercury (e.g., Hg²⁺ to Hg⁰) within thewFGD scrubber liquor. For example, one reduction reaction involves theoxidation of sulfite by ionic mercury in the wFGD to provide sulfate andelemental mercury. The result is an increase across the wFGD ofelemental mercury content in the scrubbed combustion gas, and thus adecrease in total mercury capture as measured from fossil fuel to stack.This reduction of oxidized mercury in the scrubber and subsequentrelease is known in the industry as mercury re-emission. The loss inwFGD mercury capture efficiency due to mercury re-emission will preventsome EGUs from meeting the MATS Rule, necessitating installation ofadditional equipment.

Mercury re-emission is currently addressed with the addition of certainadditives. However, in addition to controlling mercury re-emission,there remains a need to treat the scrubbing byproduct, i.e., syntheticgypsum.

BRIEF SUMMARY

The present disclosure relates to additives for mercury control, methodsof controlling mercury, and compositions comprising synthetic gypsum,mercury, and one or more of the additives described herein.

In one embodiment, a method of treating synthetic gypsum is disclosed.The method comprises transporting the synthetic gypsum from a wet fluegas desulfurizer and contacting the synthetic gypsum with an additive,the additive comprising a sulfur-containing compound.

In some embodiments, the sulfur-containing compound is selected from thegroup consisting of an inorganic sulfide, an organic sulfide, an organiccompound comprising nitrogen and sulfur, an organic compound comprisingoxygen and sulfur, a polymer comprising sulfur, and any combinationthereof.

In some embodiments, the polymer comprising sulfur is modified tocontain at least one of a sulfide and a dithiocarbamate salt group.

In some embodiments, the polymer comprising sulfur comprises about 5mole % to about 100 mole % of dithiocarbamate salt groups.

In some embodiments, the organic sulfide is selected from the groupconsisting of 2,3-dimercaptopropanol, mercaptoacetic acid,trimercaptotriazine, and any combination thereof.

In some embodiments, the polymer comprising sulfur comprises thefollowing structure:

In some embodiments, the polymer comprising sulfur comprises a weightaverage molecular weight of about 500 g/mol to about 200,000 g/mol.

In some embodiments, the polymer comprising sulfur comprises at least anacrylic-x monomer and an alkylamine, wherein the acrylic-x monomercomprises the following generic structure:

wherein X may be OR, OH, salts of OR, salts of OH, or NHR²; R¹ and R²are independently selected from H, an alkyl group, or an aryl group; andR is an alkyl group or an aryl group.

In some embodiments, the alkylamine comprises a member selected from thegroup consisting of an ethyleneamine, a polyethylenepolyamine, anethylenediamine, a diethylenetriamine, a triethylenetetraamine, atetraethylenepentamine, a pentaethylenehexamine, and any combinationthereof.

In some embodiments, the acrylic-x monomer comprises a member selectedfrom the group consisting of methyl acrylate, methyl methacrylate, ethylacrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate,acrylic acid, salts of acrylic acid, methacrylic acid, salts ofmethacrylic acid, acrylamide, methacrylamide, and any combinationthereof.

In some embodiments, the molar ratio of the acrylic-x monomer to thealkylamine is from about 0.85 to about 1.5.

In some embodiments, the additive comprises a water-soluble ethylenedichloride ammonia polymer having a molecular weight from about 500g/mol to about 10,000 g/mol and containing from about 5 to about 50 mole% of dithiocarbamate salt groups.

In some embodiments, the polymer comprising sulfur is formulated with asulfide precipitant.

In some embodiments, the polymer comprising sulfur is formed by reactingglycidyl (meth)acrylate, allyl glycidyl ether or[(vinyloxy)methyl]oxirane with ammonia or a primary amine to form afirst product, reacting the first product with one or more of acrylicacid, vinyl alcohol, vinyl acetate, acrylamide, methylacrylic acid, andmethylacrylamide to form a second product, and reacting the secondproduct with a dithiocarbamic acid salt.

In some embodiments, the synthetic gypsum comprises mercury and anamount of the additive contacting the synthetic gypsum is within a rangeof about 0.2 to about 2 moles of sulfur per mole of mercury.

In some embodiments, the additive comprises water.

In some embodiments, the synthetic gypsum is contacted by the additivein a conduit leading to a kiln.

In some embodiments, the additive comprises a compound selected from thegroup consisting of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, aderivative of α-cyclodextrin, a derivative of β-cyclodextrin, aderivative of γ-cyclodextrin, a derivatives of cyclodextrin prepared bycondensation of α-, β-, or γ-cyclodextrins with an epoxide, and anycombination thereof.

In other embodiments of the present disclosure, a composition isdisclosed. The composition comprises synthetic gypsum, mercury, and anadditive, the additive comprising a sulfur-containing compound.

In some embodiments, the sulfur-containing compound comprises a polymerincluding at least an acrylic-x monomer and an alkylamine, wherein theacrylic-x monomer comprises the following generic structure:

wherein X may be OR, OH, salts of OR, salts of OH, or NHR²;R¹ and R² are independently selected from H, an alkyl group, or an arylgroup; and R is an alkyl group or an aryl group.

In some embodiments, the polymer comprises at least one of a sulfide anda dithiocarbamate salt group.

In some embodiments, the alkylamine comprises a member selected from thegroup consisting of an ethyleneamine, a polyethylenepolyamine, anethylenediamine, a diethylenetriamine, a triethylenetetraamine, atetraethylenepentamine, a pentaethylenehexamine, and any combinationthereof.

In some embodiments, the additive comprises a water-soluble ethylenedichloride ammonia polymer having a molecular weight from about 500g/mol to about 10,000 g/mol and containing from about 5 to about 50 mole% of dithiocarbamate salt groups.

The present disclosure also provides the use of an additive for treatingsynthetic gypsum. The additive comprises a sulfur-containing compoundand is added to the synthetic gypsum that has been transported from awet flue gas desulfurizer.

The foregoing has outlined rather broadly the features and technicaladvantages of the present disclosure in order that the detaileddescription that follows may be better understood. Additional featuresand advantages of the disclosure will be described hereinafter that formthe subject of the claims of this application. It should be appreciatedby those skilled in the art that the conception and the specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other embodiments for carrying out the same purposes of thepresent disclosure. It should also be realized by those skilled in theart that such equivalent embodiments do not depart from the spirit andscope of the disclosure as set forth in the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A detailed description of the invention is hereafter described withspecific reference being made to the drawings in which:

FIG. 1 shows a graph depicting ICP-MS mercury values for gypsum solidsfrom three industrial sites (Alpha, Beta and Gamma) and reportedliterature values.

FIG. 2 depicts SEM micrographs of Beta site gypsum samples before (A)and during (B) sulfur-containing scrubber additive application and Gammasite gypsum samples before (C) and during (D) sulfur-containing scrubberadditive application.

FIGS. 3A and 3B show graphs depicting mercury dissociation (release)from Beta (FIG. 3A) and Gamma (FIG. 3B) site gypsum samples at varyingtemperature. “Pre-compliance” means before sulfur-containing scrubberadditive addition and “compliance” means during sulfur-containingscrubber additive addition. “Low ORP” is <300 mV and “High ORP” is >300mV.

FIG. 4 shows a graph depicting mercury dissociation over time at about190° C. for the beta site gypsum sample.

DETAILED DESCRIPTION

Various embodiments are described below. The relationship andfunctioning of the various components of the embodiments may better beunderstood by reference to the following detailed description. However,embodiments are not limited to those specifically described below.

Additives comprising sulfur-containing compounds are described below.Methods of treating synthetic gypsum with the additives are alsodisclosed. In addition, compositions comprising synthetic gypsum,mercury, and an additive are contemplated herein. When added tosynthetic gypsum, the additive(s) serves to thermally stabilize heavymetals, such as mercury. This thermal stabilization reduces mercuryrelease from the synthetic gypsum during processing into constructionmaterials, such as wallboard. Moreover, the additive(s) facilitateslower overall mercury emissions from the process used to manufactureconstruction materials from synthetic gypsum.

The inventors studied how mercury control additives that were applied inthe wFGD impacted downstream operations and byproducts. The byproduct ofsulfur removal via wFGDs in the case of forced oxidation scrubbing issynthetic gypsum. Synthetic gypsum is used in the production of gypsumboard and other commercial products. As a result of the study, it wasunexpectedly discovered that the byproduct synthetic gypsum quality isenhanced as a result of the application of the presently disclosedadditives comprising sulfur-containing compounds. This improvement makesthe synthetic gypsum thus formed emit less mercury to the environmentduring subsequent processing, as compared to untreated synthetic gypsum,by stabilizing the mercury in the solid.

The presently disclosed additives comprise one or more sulfur-containingcompounds. Illustrative, non-limiting examples of sulfur-containingcompounds are selected from inorganic sulfides, organic sulfides,organic compounds containing nitrogen and sulfur, organic compoundscontaining oxygen and sulfur, and low molecular weight polymerscontaining sulfur. The presently disclosed additives may comprise one ofthese compounds or any combination of these compounds. Moreover, theadditives may comprise water such that the sulfur-containing compoundsare provided as aqueous solutions.

Inorganic sulfides include, but are not limited to, aqueous sulfideions, such as NaHS. Additionally, a source of inorganic sulfides mayinclude sulfidic waste water, kraft caustic liquor, kraft carbonateliquor, potassium sulfide, thioacetamide, sodium hydrosulfide, andpotassium hydrosulfide. In some embodiments, the inorganic sulfides maybe introduced to the synthetic gypsum as an aqueous sulfide species.

Organic sulfides include, but are not limited to,2,3-dimercaptopropanol, mercaptoacetic acid, polythiocarbonate disodiumsalt, and trimercaptotriazine. Any organic sulfide known to controlmercury may be used in accordance with the present disclosure.

The low molecular weight polymers useful in connection with the presentdisclosure contain sulfur. In some embodiments, such polymers maycomprise weight-average molecular weights from about 500 g/mol to about200,000 g/mol. In certain embodiments, the low molecular weight polymerscomprise the following general structure:

In some embodiments, the polymer is derived from at least two monomers:acrylic-x and an alkylamine, wherein the “acrylic-x” has the followingformula:

X may be OR, OH, or salts thereof. X may also be NHR², wherein R¹ and R²are independently selected from H, an alkyl group, or an aryl group(substituted or unsubstituted). R is an alkyl group or an aryl group(substituted or unsubstituted). In some embodiments, R is selected fromthe group consisting of H, C₁-C₁₆ alkyl, aryl, arylalkyl, C₂-C₁₆alkenyl, C₂-C₁₆ alkynyl, heteroaryl, alkylheteroaryl, C₃-C₈ cycloalkyl.In some embodiments, R1 is selected from the group consisting of H,C₁-C₁₆ alkyl, aryl, arylalkyl, C₂-C₁₆ alkenyl, C₂-C₁₆ alkynyl,heteroaryl, alkylheteroaryl, C₃-C₈ cycloalkyl, and halogen. In someembodiments, R2 is selected from the group consisting of H, C₁-C₁₆alkyl, aryl, arylalkyl, C₂-C₁₆ alkenyl, C₂-C₁₆ alkynyl, heteroaryl,alkylheteroaryl, and hydroxyl. The polymer is modified to contain atleast one functional group capable of scavenging one or morecompositions containing one or more metals, such as mercury.

The molecular weight of the polymers can vary. For example, the targetspecies/application for the polymers can be one factor to take intoconsideration when determining an appropriate molecular weight. Anotherfactor can be monomer selection. When molecular weight is mentioned inthe present disclosure, it is referring to the weight average molecularweight of the unmodified polymer, otherwise referred to as the polymerbackbone. The functional groups that are added to the backbone are notpart of the calculation. Thus the molecular weight of the polymer withthe functional groups can far exceed the molecular weight range givenfor the polymer backbone.

In one embodiment, the molecular weight of the polymer is from about1,000 g/mol to about 16,000 g/mol. In another embodiment, the molecularweight of the polymer is from about 1,500 g/mol to about 8,000 g/mol.

Various functional groups can be utilized for mercury scavenging orscavenging of other metals in the synthetic gypsum. The polymer ismodified to contain a functional group(s) that can bind metals. In oneembodiment, the functional group contains a sulfide. In anotherembodiment, the functional group is a dithiocarbamate salt group. In oneembodiment, the functional group comprises dimethyl dithiocarbamate.

The molar amounts of the functional group relative to the total aminecontained in the unmodified polymer can vary. For example, the reactionof 3.0 molar equivalents of carbon disulfide to a 1.0:1.0 mole ratioacrylic acid/tetraethylenepentamine copolymer, which contains 4 molarequivalents of amine per repeat unit after polymerization, will resultin a polymer that is modified to contain 75 mole % dithiocarbamate saltgroups. In other words, 75% of the total amines in the unmodifiedpolymer have been converted to dithiocarbamate salt groups.

In one embodiment, the polymer has between about 5 to about 100 mole %of dithiocarbamate salt groups. In a further embodiment, the polymer hasfrom about 25 to about 90 mole % of dithiocarbamate salt groups. In yeta further embodiment, the polymer has from about 55 to about 80 mole %of dithiocarbamate salt groups.

Specific monomers for the polymer can be selected by one of ordinaryskill in the art. The alkylamines may vary. In one embodiment, thealkylamine is at least one of the following: an ethyleneamine, apolyethylenepolyamine, ethylenediamine (EDA), diethylenetriamine (DETA),triethylenetetraamine (TETA), tetraethylenepentamine (TEPA), andpentaethylenehexamine (PEHA).

The acrylic-x monomer group can vary as well. In some embodiments, theacrylic-x is at least one of the following: methyl acrylate, methylmethacrylate, ethyl acrylate, and ethyl methacrylate, propyl acrylate,and propyl methacrylate. In other embodiments, the acrylic-x is at leastone of the following: acrylic acid and salts thereof, methacrylic acidand salts thereof, acrylamide, and methacrylamide.

The molar ratio between monomers that make up the polymer, especiallyacrylic-x and alkylamine, can vary and depend upon the resultant polymerproduct that is desired. The molar ratio used is defined as the moles ofacrylic-x divided by the moles of alkylamine. In one embodiment, themolar ratio between acrylic-x and alkylamine is from about 0.85 to about1.5. In another embodiment, the molar ratio between acrylic-x andalkylamine is from about 1.0 to about 1.2.

Various combinations of acrylic-x and alkylamines are contemplated bythe present disclosure, in addition to the associated molecular weightof the polymers. In one embodiment, the acrylic-x is an acrylic esterand the alkylamine is PEHA, TEPA, DETA, TETA, or EDA. In a furtherembodiment, the molar ratio between acrylic-x and alkylamine is fromabout 0.85 to about 1.5. In another embodiment, the molecular weight canencompass ranges from about 500 g/mol to about 200,000 g/mol, from about1,000 g/mol to about 16,000 g/mol, or from about 1,500 g/mol to about8,000 g/mol.

In certain embodiments, the acrylic ester can be at least one of thefollowing: methyl acrylate, methyl methacrylate, ethyl acrylate, andethyl methacrylate, propyl acrylate, and propyl methacrylate, which iscombined with at least one of the alkylamines, which includes PEHA,TEPA, DETA, TETA, or EDA. In some embodiments, the resulting polymer ismodified to contain the following ranges of dithiocarbamate salt groups:from about 5 to about 100 mole %, from about 25 to about 90 mole %, andfrom about 55 to about 80 mole %.

In another embodiment, the acrylic-x is an acrylic amide and thealkylamine is PEHA, TEPA, DETA, TETA, or EDA. In a further embodiment,the molar ratio between acrylic-x and alkylamine is from about 0.85 toabout 1.5. The acrylic amide can be at least one or a combination ofacrylamide and methacrylamide, which is combined with at least one ofthe following alkylamines: PEHA, TEPA, DETA, TETA, or EDA.

In another embodiment, the acrylic-x is an acrylic acid (or salt ofacrylic acid) and the alkylamine is PEHA, TEPA, DETA, TETA, or EDA. Inyet a further embodiment, the acrylic acid can be at least one or acombination of acrylic acid or salts thereof and methacrylic acid orsalts thereof, which is combined with at least one of the followingalkylamines: PEHA, TEPA, DETA, TETA, or EDA.

Other monomers can be integrated into the polymer backbone in additionto the constituent monomers, acrylic-x and alkylamine. A condensationpolymer reaction scheme can be utilized to make the basic polymerbackbone chain. Various other synthetic methods can be utilized tofunctionalize the polymer with, for example, dithiocarbamate and/orother known mercury scavenging functional groups. One of ordinary skillin the art can functionalize the polymer without undue experimentation.

Moreover, the low molecular weight polymer of the present disclosure canbe formulated with other polymers, such as those disclosed in U.S. Pat.No. 5,164,095, which is incorporated herein by reference, which includea water soluble ethylene dichloride ammonia polymer having a molecularweight between 500 g/mol and 100,000 g/mol and contain from 5 to 50 mole% of dithiocarbamate salt groups. Also, the low molecular weight polymercan be formulated with other small molecule sulfide precipitants, suchas sodium sulfide, sodium hydrosulfide, TMT-15® (sodium or calcium saltsof trimercapto-s-triazine; Evonik Industries Corporation 17211Camberwell Green Lane, Houston, Tex. 77070, USA),dimethyldithiocarbamate, and/or diethyldithiocarbamate.

In certain embodiments, the low molecular weight polymer of the presentdisclosure comprises a water-soluble ethylene dichloride ammonia polymerhaving a molecular weight from about 500 g/mol to about 10,000 g/mol andcontaining from about 5 to about 50 mole % of dithiocarbamate saltgroups. The salts include, but are not limited to, alkaline and alkaliearth metals, such as sodium, lithium, potassium, or calcium.

In still further embodiments the sulfur-containing compounds may be oneor more polymers obtained by: 1) reacting glycidyl (meth)acrylate, allylglycidyl ether, or [(vinyloxy)methyl]oxirane with ammonia or a primaryamine to form a first product, 2) reacting the first product with one ormore of acrylic acid, vinyl alcohol, vinyl acetate, acrylamide,methylacrylic acid, and methylacrylamide to form a second product, and3) reacting the second product with a dithiocarbamic acid salt.

One or more of the sulfur-containing compounds may comprise any of thefollowing general structural formulas I, II, and III:

wherein R₁ is —OM or —NH₂; R₂, R₉, R₁₂, and R₁₆ are independentlyhydrogen, or a methyl group; R₃, R₄, R₇, R₈, R₁₀, R₁₁, R₁₇, and R₁₈ areindependently hydrogen, a methyl group, or —COOH; R₅, R₁₃, and R₁₄ areindependently selected from:

R₆ is H,

R₁₅ is —CSSM,

and M is monovalent cation.

The additive described herein may comprise one or more sulfur-containingcompounds disclosed in U.S. Pat. No. 8,632,742, the disclosure of whichis incorporated by reference into the present application.

Additionally, the presently disclosed additive may comprise one or morecyclodextrin compounds, such as α-cyclodextrin, β-cyclodextrin,γ-cyclodextrin, derivatives of α-cyclodextrin, derivatives ofβ-cyclodextrin, derivatives of γ-cyclodextrin, derivatives ofcyclodextrin prepared by condensation of α-, β-, or γ-cyclodextrins withepoxides, and mixtures thereof. The additive may comprise anycyclodextrin compound, such as those disclosed in U.S. Pat. No.9,120,055, the disclosure of which is incorporated by reference into thepresent application.

The amount of the additive comprising one or more sulfur-containingcompounds to be added to the synthetic gypsum can vary widely. In someembodiments, the amount to be added depends upon the amount of mercuryin the synthetic gypsum. The calculation of dosage amounts can be donewithout undue experimentation.

In one embodiment, the amount of the additive comprisingsulfur-containing compounds added to the synthetic gypsum is within therange of about 0.2 to about 2 moles of sulfur per mole of mercury. Insome embodiments, the additive is applied at a ratio of about 1:1 toabout 2000:1, by weight, of the additive to the weight of mercury beingcaptured from the synthetic gypsum. Exemplary ratios include from about5:1 to about 1000:1 and from about 5:1 to about 500:1.

The present disclosure contemplates adding the additive comprisingsulfur-containing compounds directly to synthetic gypsum. For example, awFGD includes a solid waste side, where the synthetic gypsum byproductexits the wFGD. The additive comprising the sulfur-containing compoundcan be added to the synthetic gypsum at this location. In someembodiments, the additive is only added to the synthetic gypsum after(and not before) it exits a wFGD. Additionally, gypsum plants, whichmake construction materials, generally include conduits comprisingstreams of synthetic gypsum used to form the construction materials. Thestreams may comprise from about 1% to about 100% synthetic gypsum. Oneor more of the conduits may feed into a kiln. The presently disclosedadditives can be added to the gypsum stream in a conduit.

In general, the presently disclosed additives comprisingsulfur-containing compounds can be added to the synthetic gypsum at anytime after the gypsum exits the wFGD, such as during a gypsummanufacturing process. As such, while the prior art may seek to controlmercury emission at power plants, aspects of the present disclosure canbe used to control mercury emission at gypsum plants. While developingthe presently disclosed technology, the inventors unexpectedlydiscovered that mercury is not released from the synthetic gypsum attemperatures up to about 190° C. because the mercury is stabilized bythe presently disclosed additives after they are added to the syntheticgypsum.

EXAMPLES

Various additives were tested by the inventors to prove the inventiveconcept of the present application. For example, some of the testedadditives comprised various polymers. Some of the polymers were derivedfrom at least two monomers: acrylic-x and an alkylamine. Some of thepolymers were modified to contain a particular functional group. In someof the additives, the molar ratio between acrylic-x and alkylamine wasfrom about 0.85 to about 1.5. In some of the additives, the alkylaminewas selected from an ethyleneamine, a polyethylenepolyamine,ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetraamine(TETA), tetraethylenepetamine (TEPA), pentaethylenehexamine (PEHA), andany combination thereof. In some of the additives, the acrylic-x wasselected from methyl acrylate, methyl methacrylate, ethyl acrylate,ethyl methacrylate, propyl acrylate, propyl methacrylate, and anycombination thereof. In some of the additives, the functional groupcomprised a sulfide containing chemistry and in other additives, thefunctional group comprised a dithiocarbamate salt group.

In some experiments, the inventors tested a polymer additive wherein theacrylic-x comprised acrylic acid, the alkylamine comprised TEPA, and theratio of acrylic-x:alkylamine was 1.0. The average weight molecularweight of the polymer backbone (Poly(Acrylic Acid/TEPA) relative tomeasurement used was about 5,000 Daltons. The polymer included adithiocarbamate functional group (reaction of polymer backbone withcarbon disulfide and caustic) reacted to about 70 mole % of the totalamine in the polymer backbone. The average weight molecular weight ofmodified polymer backbone (70 mole % carbondisulfide-modified-Poly(Acrylic Acid/TEPA)) cannot be measured due tomethod/equipment limitations but it was estimated to be about 10,700Daltons. In the experiments described below, this particular additive isreferred to as “sulfur-containing scrubber additive.”

Gypsum samples were taken from different coal-fired power plant wFGDslurry systems both before addition of a sulfur-containing scrubberadditive and during application of sulfur-containing scrubber additivewhere the plants were within MATS compliance. Samples were then analyzedby thermal dissociation of mercury from the sample and then analyzed bya specialized elemental mercury spectrometer. The temperatures analyzedduring thermal dissociation were about 125, about 190, about 350 andabout 680° C. Samples were also analyzed by inductively coupledplasma-mass spectrometry (ICP-MS) to determine total mercury content inthe gypsum and scanning electron microscopy (SEM) for morphologychanges. Subsequently, a toxicity characteristic leaching procedure(TCLP) was carried out to determine if the samples would leach toxicmaterials in a landfill. Three different commercial units were sampled;their general configurations can be seen in Table 1.

TABLE 1 General configurations of the power generation units for theWFGD scrubber slurry samples analyzed. Unit Coal SCR AQCDs Fines AlphaBituminous Yes FF, LSFO Hydroclones Beta Bituminous No ESP(H); LSFOHydroclones Gamma Bituminous Yes ESP(H); LSFO Hydroclones AQCDs—airquality control devices, FF—fabric filter, LSFO—limestone scrubber withforced air oxidation, ESP—electrostatic precipitator.

Mercury content in the gypsum samples was compared to reportedliterature values from other commercial sources. The reported mercurylevels in the samples compared well to those from the three commercialsites using ICP-MS (FIG. 1). Application of a sulfur-containing scrubberadditive did not increase the mercury content levels. All mercury levelsin the gypsum samples were typical of those seen in gypsum from othercoal-fired power plants.

The morphology and size of the gypsum particles was also not changed bythe application of a sulfur-containing scrubber additive while both theBeta and Gamma units were within MATS compliance, as seen in the SEMmicrographs in FIG. 2.

TCLP testing of both the Beta and Gamma sites' gypsum, before and duringsulfur-containing scrubber additive addition, found no change in themercury leaching and all samples were below the RCRA limit of 200,000ppt (Table 2).

TABLE 2 TCLP data for mercury leaching in gypsum samples. Average SystemCondition (ppt) StdDev % RSD Beta Site Pre- 10.3 4.03 39.1 ComplianceMATS 11.5 5.50 47.9 Compliance Gamma Site Pre- 21.7 8.98 41.3 ComplianceMATS 27.0 9.42 34.9 Compliance Pre-compliance = before sulfur-containingscrubber additive addition. MATS compliance = during sulfur-containingscrubber additive addition.

The amount of the additive that was used in the tests was not preciselyknown. These gypsum samples were taken from commercial units using theinventor's technology to meet MATS compliance. The dosage isautomatically fed based on a number of factors, including ORP andmegawatt load of the unit (based on, for example, U.S. Pat. No.8,632,742, which is incorporated by reference into the presentapplication in its entirety). The gypsum taken from these plants is thesame gypsum sold to wallboard manufacturers so this is a real worldapplication and test of the technology.

Typical wallboard manufacturing employing gypsum has a maximum temp of166° C. for a 15 minute dwell. During the thermal dissociation ofmercury from the gypsum analysis, a temperature of about 190° C. wasused to encompass all process steps during a typical wall boardproduction. In FIGS. 3A and 3B, both Beta and Gamma site gypsum wasanalyzed for mercury dissociation. The Beta and Gamma site gypsumsamples show no change in mercury dissociation at about 190° C. andlower. During gypsum processing there should be no change. Aninteresting trend was seen with oxidative reduction potential (ORP) athigher temperatures. As ORP decreases, more mercury is typically foundin the solid phase in a wFGD scrubber slurry. In FIG. 4, the mercurydissociation from the beta site gypsum can be seen for a number ofsamples at about 190° C. From these plots we can determine that at about190° C. and lower, a sulfur-containing scrubber additive increases thestability of mercury in gypsum and increases the temperature at whichmercury will dissociate from the gypsum.

Any composition (or additive) disclosed herein may comprise, consist of,or consist essentially of any of the compounds/components disclosedherein. In accordance with the present disclosure, the phrases “consistessentially of,” “consists essentially of,” “consisting essentially of,”and the like limit the scope of a claim to the specified materials orsteps and those materials or steps that do not materially affect thebasic and novel characteristic(s) of the claimed invention.

As used herein, the term “about” refers to the cited value being withinthe errors arising from the standard deviation found in their respectivetesting measurements, and if those errors cannot be determined, then“about” refers to within 10% of the cited value.

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While this invention may be embodied in many differentforms, specific preferred embodiments of the invention are describedherein. The present disclosure is an exemplification of the principlesof the invention and is not intended to limit the invention to theparticular embodiments illustrated. In addition, unless expressly statedto the contrary, use of the term “a” is intended to include “at leastone” or “one or more.” For example, “a device” is intended to include“at least one device” or “one or more devices.”

Any ranges given either in absolute terms or in approximate terms areintended to encompass both, and any definitions used herein are intendedto be clarifying and not limiting. Notwithstanding that the numericalranges and parameters setting forth the broad scope of the invention areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical value, however,inherently contains certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.Moreover, all ranges disclosed herein are to be understood to encompassany and all subranges (including all fractional and whole values)subsumed therein.

Furthermore, the invention encompasses any and all possible combinationsof some or all of the various embodiments described herein. It shouldalso be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the invention and withoutdiminishing its intended advantages. It is therefore intended that suchchanges and modifications be covered by the appended claims.

What is claimed is:
 1. A method of treating synthetic gypsum,comprising: transporting the synthetic gypsum from a wet flue gasdesulfurizer; and contacting the synthetic gypsum with an additive, theadditive comprising a sulfur-containing compound and water, wherein thesulfur-containing compound is a polymer comprising sulfur that ismodified to contain at least one of a sulfide and a dithiocarbamate saltgroup.
 2. The method of claim 1, wherein the polymer comprising sulfurcomprises about 5 mole % to about 100 mole % of dithiocarbamate saltgroups.
 3. The method of claim 1, wherein the polymer comprising sulfurcomprises the following structure:


4. The method of claim 1, wherein the polymer comprising sulfur isformulated with a sulfide precipitant.
 5. The method of claim 1, whereinthe polymer comprising sulfur is formed by reacting glycidyl(meth)acrylate, allyl glycidyl ether or [(vinyloxy)methyl]oxirane withammonia or a primary amine to form a first product, reacting the firstproduct with one or more of acrylic acid, vinyl alcohol, vinyl acetate,acrylamide, methylacrylic acid, and methylacrylamide to form a secondproduct, and reacting the second product with a dithiocarbamic acidsalt.
 6. The method of claim 1, wherein the synthetic gypsum iscontacted by the additive in a conduit leading to a kiln.
 7. A method oftreating synthetic gypsum, comprising: transporting the synthetic gypsumfrom a wet flue gas desulfurizer; and contacting the synthetic gypsumwith an additive, the additive comprising a sulfur-containing compound,wherein the sulfur-containing compound is a polymer comprising sulfurthat comprises a weight average molecular weight of about 500 g/mol toabout 200,000 g/mol.
 8. A composition comprising synthetic gypsum,mercury, and an additive, the additive comprising a sulfur-containingcompound, wherein the sulfur-containing compound comprises a polymerincluding at least an acrylic-x monomer and an alkylamine, wherein theacrylic-x monomer comprises the following generic structure:

wherein X may be OR, OH, salts of OR, salts of OH, or NHR²; R¹ and R²are independently selected from H, an alkyl group, or an aryl group; andR is an alkyl group or an aryl group.
 9. The composition of claim 8,wherein the polymer comprises at least one of a sulfide and adithiocarbamate salt group.
 10. The composition of claim 8, wherein thealkylamine comprises a member selected from the group consisting of anethyleneamine, a polyethylenepolyamine, an ethylenediamine, adiethylenetriamine, a triethylenetetraamine, a tetraethylenepentamine, apentaethylenehexamine, and any combination thereof.